<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <script>
        var foo = true,
            bar = 10
        if (foo) {
            var tub = 20
        }
        if (tub > bar) {
            // 执行一些操作
            console.log(tub);
        }
    </script>
</body>

</html>